However, the region's "non-negative" test results decreased from 5 per cent to 3.9 per cent, and were down nationwide from 6.4 per cent to 5.5 per cent.
A non-negative test indicates the initial presence of drugs, at which point the test is forwarded to an accredited laboratory for confirmation testing.
The most commonly detected drug in Central workers was cannabis, which turned up in more than 60 per cent of non-negative tests.
Mr Silcock said his company had not experienced problems with employees failing tests, but did it as general good practice with new employees for health and safety. "With the stuff that's around these days you've still got to play it safe."
If a driver was under the influence of drugs, the effect was the same as drink driving, he said. Workplace drug testing was "becoming more of a norm" in Wanganui, and had increased over recent years.
"It's just to keep everybody safe because it all comes back down to that chain of responsibility [for employers]."
New Zealand was "miles behind the times" for drug tests, with Australia and Europe well ahead, he said.
NZDDA head Chris Hilson said the continued rise in the number of on-site workplace drug and alcohol tests showed employers were taking workplace safety seriously.
Not only were employers in safety-sensitive industries increasing drug and alcohol testing, but more white-collar employers were also carrying out substance screening, he said.
"Whether you're in the forestry industry, run a transport business, or in the financial sector, it's vital for your organisation that your employees are working unimpaired and without risk."
Cannabis was still the most common drug nationwide identified in non-negative tests (71 per cent) and was most frequently detected in "traditional" growing areas such as Northland, Waikato, Bay of Plenty and the North Island's East Cape.
Methamphetamine detection was up to 7 per cent from 6 per cent nationwide.
Synthetic cannabis testing results were included for the first time with 3.3 per cent testing non-negative - the highest rates in the mining/oil/gas sector. The tourism industry, in particular, recorded a high rate of cannabis and amphetamine use.